1. Field of the Invention
This disclosure relates to a single-crystal graphene sheet and a process of preparing the same.
2. Description of the Related Art
Generally, graphite is a stack of two-dimensional graphene sheets formed from a planar array of carbon atoms bonded to form hexagonal structures. Recently, testing of graphene sheets revealed beneficial properties of single or multiple-layered graphene sheets. One beneficial property of graphene is that electrons flow in an entirely unhindered fashion in a graphene sheet, which is to say that the electrons flow at the velocity of light in a vacuum. In addition, graphene sheets exhibit an unusual half-integer quantum Hall effect for both electrons and holes.
The electron mobility of conventional graphene sheets is about 20,000 to 50,000 cm2/Vs.
In some applications carbon nanotubes can be used as a conductor. However, carbon nanotubes are expensive due to low yields during synthesis and purification processes. Also single wall carbon nanotubes exhibit different metallic and semiconducting characteristics according to their chirality and diameter. Furthermore, single wall carbon nanotubes having identical semiconducting characteristics have different band gap energies depending on their chirality and diameter. Thus, single wall carbon nanotubes are preferably separated from each other in order to obtain the desired semiconducting or metallic properties. However, separating single wall carbon nanotubes can be problematic.
On the other hand, it is advantageous to use graphene sheets in a device, because graphene sheets can be engineered to exhibit the desired electrical characteristics by arranging the graphene sheets so that their crystallographic orientation is in a selected direction since the electrical characteristics of graphene depend on crystallographic orientation. It is envisaged that the characteristics of graphene sheets can be applied to future carbonaceous electrical devices or carbonaceous electromagnetic devices.
Graphene sheets can be prepared using a micromechanical method or by SiC thermal decomposition. According to the micromechanical method, a graphene sheet can be separated from graphite attached to the surface of Scotch™ tape by attaching the tape to a graphite sample and detaching the tape. In this case, the separated graphene sheet does not include a uniform number of layers, and the ripped portions do not have a uniform shape. Furthermore, a large-sized graphene sheet cannot be prepared using the micromechanical method. Meanwhile, in SiC thermal decomposition, a SiC single crystal is heated to remove Si by decomposition of the SiC on the surface thereof, the residual carbon then forming a graphene sheet. However, the SiC single crystal material used as a starting material in SiC thermal decomposition is very expensive, and formation of a large-sized graphene sheet can be problematic.
Accordingly, a process to economically and reproducibly prepare a large-size graphene sheet that has the desired electrical properties is needed.